JP3264004B2 - Vacuum condenser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable vacuum capacitor used for adjusting the impedance of a high frequency power supply of a semiconductor manufacturing apparatus.

[0002]

2. Description of the Related Art FIG. 1 is a cross-sectional view of a general variable vacuum capacitor of this type. For example, a side face is formed by ceramics 12 having copper flanges 11a and 11b at both ends thereof. Are fixed conductor 13 and metal lid 14
To form a vacuum container 10 for filling a high-yield vacuum dielectric.

A plurality of substantially cylindrical electrode plates having different inner diameters are provided concentrically at regular intervals inside the fixed conductor 13 to form a fixed electrode 15.
The movable electrode 16 is formed by a plurality of cylindrical electrode plates having different inner diameters which are inserted into and removed from each electrode gap in a non-contact state. This movable electrode 16 is provided on a movable conductor 18.

The movable conductor 18 has a hollow lead 18a on the back side of the movable electrode 16, and the side surface of the hollow lead is slidably supported by a bearing 17 as shown in FIG. . An internal thread 18b is formed on the inner wall of the end of the hollow lead 18a.

Reference numeral 19 denotes a capacitance adjusting screw,
a and a male screw 19b inserted into the female screw 18b. As shown in the figure, the capacitance adjusting screw 19 is supported by a support formed at a substantially central portion of the lid 14, that is, a screw receiving portion 20 and a thrust bearing 21 for reducing rotational torque. By rotating the head 19a manually or using a motor or the like, the movable conductor 18 is rotated.
Up and down. As a result, the crossing area between the fixed electrode 15 and the movable electrode 16 changes, so that when a voltage having a different polarity is applied to both the electrodes 15, 16, the value of the capacitance generated between the electrodes is continuously changed. be able to.

Reference numeral 22 denotes a bellows made of a soft metal, one end of which is joined to the inner wall of the lid 14 and the bearing 17 so that the movable conductor 18 (movable electrode 16) can move up and down while keeping the inside of the vacuum vessel 10 airtight. And move the other end to the movable conductor 1
8. There is also a structure in which the other end is joined to the surface of the hollow lead portion 18a. Hollow lead 18a
Since the lubricating oil is insulated between the bellows 22 and the bearing 17 for guiding the bellows, the bellows 22 is configured to be energized inside the vacuum vessel 10. That is, the bellows 22 also serves as a current path between an external power supply terminal (not shown) provided on the lid 14 and the movable electrode 16.

[0007]

The characteristics required for a vacuum capacitor include the following two.

(1) Low loss and low heat generation during energization (2) Long life In a vacuum capacitor having the above structure, the material of the bellows 22 has a great influence on the above characteristics. Conventionally, bellows 2
As the materials used for No. 2, there are a copper-based material such as phosphor bronze and beryllium copper and a stainless-based material such as SUS304L, but both have advantages and disadvantages, and cannot simultaneously satisfy the above required characteristics. . For example, a stainless steel bellows has a longer life than a copper bellows. However, as is clear from the current-temperature characteristics diagram of the phosphor bronze bellows and the SUS304L bellows in FIG. Fever was inevitable.

For this reason, conventionally, although the problem of the life remains,
Phosphor bronze bellows having excellent current carrying capacity was used.

The present invention has been made under such a background, and an object of the present invention is to provide a vacuum capacitor having a structure that simultaneously satisfies the above required characteristics.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a vacuum pump having a bellows which keeps the inside of a vacuum container airtight following a displacement of a movable electrode and also serves as a current path to an external power supply terminal. The capacitor is characterized in that the bellows is made of a stainless steel plated with a copper-based material or a silver-based material. It is assumed that the thickness of this plating film is 10 microns or more.

[0012]

In general, vacuum capacitors are used for high frequency applications. When the frequency of the current applied is of the order of a few MH _Z, because the current is concentrated on only the surface of the bellows due to the skin effect, the plating film of high copper-based material or a silver-based material having conductivity to the surface portion This makes it easier for the current to flow. On the other hand, since stainless steel has a long life, a bellows having both improved energizing ability and life can be obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. Since the present invention is an improvement of the conventional vacuum capacitor, the description of the same components as those shown in FIG. 1 will be omitted, and only different portions will be described.

In this embodiment, the bellows 22 is made of stainless steel plated with copper (Cu) in the vacuum capacitor having the structure shown in FIG. General-purpose SUS304L is used for stainless steel.

FIG. 3 is a graph showing the relationship between the current flow and the surface temperature of the vacuum capacitor according to the present embodiment.
Examples in the case of 10 μm, 20 μm and 30 μm are shown by solid lines (1) to (4), respectively. As a comparative example, the value of the conventional phosphor bronze bellows shown in FIG. 2 is indicated by a broken line. These values are
Capacitance: 500 [pF], operating frequency: 13.56
[MH _Z ], energizing current I (= ωCV: ω is angular frequency, C
Is an example in which the capacitance is varied and V is the applied voltage.

Referring to FIG. 3, when the thickness of the plating film is 10
It can be seen that when μ is, the current-carrying capacity is almost the same as that of the phosphor bronze bellows, and when 20 μm and 30 μm, the current-carrying capacity exceeds that of the phosphor bronze bellows. This is because the energizing current is concentrated on the very surface of the bellows due to the skin effect, and a highly conductive plating film becomes effective. This suppresses a rise in temperature during energization, and increases the allowable maximum current value.

FIG. 4 is a graph showing the relationship between the thickness of the plating film and the service life. In addition to the plating film having the above thickness, examples of a phosphor bronze bellows and an SUS304L bellows without a plating film are also listed as comparative examples. In the drawing, the life on the vertical axis is shown as a multiple of the case where the phosphor bronze bellows is set to 1.

Referring to FIG. 4, it can be seen that the service life of the bellows decreases as the plating film becomes thicker, but still has a service life several times that of the phosphor bronze bellows. this is,
Due to the long life of SUS304L itself.

Accordingly, by making the thickness of the plating film 10 μm or more, it is possible to extend the life of the vacuum capacitor, reduce the loss, and suppress heat generation during energization, and obtain a vacuum capacitor that simultaneously satisfies the conventional required characteristics. .

Although the above is an example of the case where copper (Cu) plating is performed, another copper-based material having substantially the same conductivity as the material of the plating film may be used. Further, if a plating film is formed with a silver-based material such as pure silver having higher conductivity, a bellows having more excellent current-carrying ability can be obtained, which can contribute to improvement of the characteristics of the vacuum capacitor.

[0021]

As described above, according to the present invention, the bellows which keeps the inside of the vacuum vessel airtight and follows the displacement of the movable electrode and also serves as a current path to the external power supply terminal is made of a copper-based material or a silver-based bellows. Since it is made of a stainless steel plated with a material, it has the effect of prolonging its life and preventing heat generation during energization. Also, the thickness of the plating film should be 10
By setting the diameter to a micron or more, the current-carrying ability is improved, and the maximum allowable current value of the vacuum capacitor is increased.

Therefore, when such a vacuum condenser is housed in the apparatus, cooling of the apparatus is not required, and the reliability of the apparatus can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a variable vacuum capacitor to which the present invention is applied.

FIG. 2 is a diagram showing current-surface temperature characteristics of a conventional vacuum capacitor using a stainless steel bellows and a phosphor bronze bellows.

FIG. 3 is a graph showing a comparison between a current flowing through a vacuum capacitor and a surface temperature characteristic of a bellows according to an embodiment of the present invention and a conventional bellows.

FIG. 4 is a diagram showing a relationship between plating thickness and life of a vacuum capacitor using a bellows according to an embodiment of the present invention and a conventional bellows.

[Explanation of symbols]

 10: vacuum vessel 16: movable electrode 22: bellows

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-U 4-74416 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01G 5/14 H01G 5/01

Claims (3)

(57) [Claims] 1. A vacuum capacitor having a bellows which keeps the inside of a vacuum vessel airtight following a displacement of a movable electrode and also serves as a current path to an external power supply terminal. A vacuum capacitor characterized by being made of stainless steel. 2. A vacuum capacitor having a bellows which keeps the inside of a vacuum vessel airtight following a displacement of a movable electrode and also serves as a current path to an external power supply terminal, wherein said bellows is coated with a silver-based plating film. A vacuum capacitor characterized by being made of stainless steel. 3. The vacuum capacitor according to claim 1, wherein the thickness of the plating film is 10 μm or more.